scalp.cor: plot the timepoint correlations between ERPs and an external...
In erpR: Event-Related Potentials (ERP) Analysis, Graphics and Utility Functions

Description Usage Arguments Details Value Author(s) See Also Examples

This function performs a series of correlations on each timepoint between ERP voltages and an external (typically a behavioural) variable. The set of ERP data frames is specified by base and numbers. The external variable is specified as a vector (of length equal to numbers) in the argument external. A scalp plot of the results is returned.

scalp.cor(base, numbers, external = NULL, alpha = 0.05, 
method = c("pearson", "kendall", "spearman"), sig = NULL, 
erplist = NULL, smo = NULL, layout = 1, ylims = "auto",
 yrev = TRUE, startmsec = NULL, endmsec = NULL, lwd = c(1, 1), 
 lty = c(1, 1), col = "blue", legend = TRUE, legend.lab = "default",
 t.axis=NULL, scalp.array=NULL)

`base`	a string indicating the beginning of the name of the set of ERP data frames.
`numbers`	the numbers of the subjects of the set of ERP data frames .
`external`	a vector indicating the values of the external variable (typically a behavioural variable). This vector must be of the same length of `numbers`
`alpha`	the alpha of the correlation tests.
`method`	the method of the correlations. Available methods are `"pearson", "kendall", "spearman"`.
`sig`	if `NULL`, then a series of correlations is computed. If an appropriate object is specified (i.e. an object returned by `scalp.cor` or `erp.cor`) then the results are retrieved by this object and the function simply plots the results.
`erplist`	a list containing ERP data frames.
`smo`	the smoothing parameter to apply (see `smooth.spline`). Default is `NULL` and no smoothing is applied.
`layout`	A number indicating the layout of electrodes to be plotted. Currently only few default layouts are supported (a number from 1 to 5). Alternatively, a character vector specifying the layout may be supplied (see `Details`).
`ylims`	a number indicating the upper and lower limits of the y-axis. If "auto", the function calculates the y limits automatically.
`yrev`	logical. If `TRUE`, the y-axis is plotted with the negative values upward.
`startmsec`	the start time (in ms) of the ERP vector
`endmsec`	the end time (in ms) of the ERP vector
`lwd`	A vector specifying the line width to be associated with each ERP data frame specfied in `categ`
`lty`	A vector specifying the line types to be associated with each ERP data frame specfied in `categ`
`col`	the color of the ERP waveform.
`legend`	logical. If `TRUE`, a legend with object names is drawn in the top-right corner of the array.
`legend.lab`	the legend labels. If "default", the names are retrieved from the `categ` argument.
`t.axis`	the position of the ticks on an additional axis indicating the time. This axis is plotted in the bottom-left corner of the plot array.
`scalp.array`	This argument is vector of two values indicating the number of panels of the plot, as number of rows and number of columns respectively. If a default layout is specified, the number of panels is automatically computed. See also `Details`.

The layout parameter can be a number (from 1 to 5), that specifies some default electrode arrangements (currently only a few default arrangements are supported). Otherwise, the argument may be a character vector indicating the names of the electrodes to be plotted. The plot is divided in a number of panels as specified in scalp.array. The names specified will be plotted from top to bottom and from left to right. If "blank" is specified an empty panel will be plotted. If "xaxis" is specified a x axis indicating time will be plotted. If "yaxis" is specified a y axis indicating voltage will be plotted.

The function plots a scalp map of ERP waveforms in an array resembling the topographic locations of the electrodes on the scalp. The waveforms represent an average of the first set of specified data frames. Timepoints with a positive (and significant) correlation are highlighted by red bars. Timepoints with a negative (and significant) correlation are highlighted by blue bars. The function also returns an object with the results of the correlations. This object can be used for future plots with erp.cor or scalp.cor, by specifying it as the argument sig.

Giorgio Arcara

erp.cor, ~~~

## Not run: 
data(erplistExample)

#generate an hypothetic external variables
RT=rnorm(20, mean=500, sd=200)

scalp.cor("Exp1_word_subj", 1:20, external = RT, layout=1, 
erplist=erplistExample, ylim=10, legend=TRUE)

## End(Not run)